The invention relates generally to telecommunication networks. More particularly, the invention concerns a mechanism for physically limiting the scope of multicast messages in such networks.
Telecommunication networks for mobile devices generally allow mobile devices to move geographically by xe2x80x9chanding offxe2x80x9d localized communication links among transmission towers and associated base stations. For example, such networks allow Internet Protocol-enabled devices such as wireless Personal Digital Assistants (PDAs) and mobile computers to move about geographically dispersed areas while maintaining a connection to the Internet.
As is well known, mobile terminals can be served by one or more access routers that service terminals within a particular area. Such access routers allow the mobile terminals to access one or more computer networks, such as the Internet, using mobile IP protocols or other protocols. Mobile terminals may communicate using one of various access technologies, such as GPRS, Bluetooth, or others.
As mobile services have become more widespread, the need has increased for users of mobile terminals to have access to devices that are located within a reasonably close geographic proximity to the user at a particular point in time. For example, the user of a wireless PDA may move into an office building and have a need to print out a document at a printer located in the office building. Aside from determining the precise geographic location of the user and all printers in the building (e.g., using GPS technology), there is no easy way to determine which printer or printers might be available for printing the document, particularly if devices within the building are connected through a different administrative domain from the access router that is serving the mobile terminal. Although multicast messages can be used to send service inquiries to destinations of indeterminate specificity, using such messages to locate a xe2x80x9cnearbyxe2x80x9d printer would not be feasible.
FIG. 1 illustrates the nature of the problem referred to above. Suppose that the user of a wireless PDA 100 moves into an area served by access router 101, which is coupled to a network 105 and ultimately to the Internet 106. Suppose further that a Bluetooth-enabled printer 102 is located within a close geographic proximity to PDA 100, illustrated by dashed line 104, but is serviced by a different access router 103, using a different access technology (e.g., Bluetooth). If the user of PDA 100 wants to print a document to the nearest printer, there is no easy way for the system to determine that the user should print to printer 102. The problem may be compounded by the fact that the addresses used to communicate with access router 101 and 103 lie in different administrative domains; i.e., they are xe2x80x9cadministratively scopedxe2x80x9d rather than geographically or physically scoped.
The Internet Engineering Task Force has defined the Service Location Protocol (RFC 2165) as a standard way of discovering services in a network. Suppose that PDA 100 or access router 101 were to send a message to a multicast address requesting information on printers or other devices that are available to print a document. Conventional multicast routing protocols rely on administrative scoping rules to determine where such a message should be sent. For example, RFC 2365 (xe2x80x9cAdministratively Scoped IP Multicast,xe2x80x9d July 1998), published by the Internet Engineering Task Force, defines a local administratively scoped multicast space. The protocol is unable to determine that printer 102 is geographically close to PDA 100 because they are in different administrative domains (and possibly served by different access technologies, such as wireless LAN technology for PDA 100 and Bluetooth for printer 102). Devices such as access routers that are physically close to the mobile terminal may be many xe2x80x9chopsxe2x80x9d away in the IP network topology, and therefore do not appear to be visible to the mobile terminal.
Consequently, a need exists for a mechanism to permit mobile devices to identify other devices that are in the same geographic vicinity even though they may reside within different administrative domains. A further need exists to permit mobile devices to send multicast messages to devices within a particular geographic area irrespective of administrative domains that are associated with the devices.
The invention provides a system and method for multicast packet delivery that is based on physical neighborhood information. Each of a plurality of access routers maintains information concerning neighboring devices (e.g., access routers).
Multicast packets arriving at an access router are classified as either physically scoped or administratively scoped. Physically scoped packets are xe2x80x9ctunneledxe2x80x9d by encapsulating them in a unicast packet, based on locally available physical neighborhood information, and sent via unicast to physically adjacent access routers.
Administratively scoped packets are handled using conventional administrative scoping protocols.
Devices that transmit packets to an access router indicate whether each packet should be administratively or physically scoped. In one variation, physical scoping is determined by the sender specifying a maximum number of hops between access routers. A device can transmit packets to a nearby device by transmitting a physically scoped multicast packet.
Other features and advantages of the invention will become apparent through the following detailed description, the figures, and the claims.